In the construction of bridges and other structures in which pile supports are driven into the earth and are used as supports for the bridge, etc., it is common to form abutment walls about the piles and to backfill the space between abutment walls and the piles with backfilled earthen materials and other materials. For example, U.S. Pat. No. 3,981,038 discloses a backfilled barrier wall formed of panels mounted one upon the other and held together with elongated reinforcing straps. As the wall is constructed, the backfilled earthen material is placed in layers beside the wall about the supporting piles of the bridge abutment. These constructions are referred to in the industry as Mechanically Stabilized Earth (MSE) wall structures.
One of the problems encountered with bridges and other structures supported by piles with backfilled earthen materials placed about the piles is that the backfilled earthen materials placed about the pile tend to settle over a length of time, and the downward movement of the backfilled earthen materials applies an adverse downward load to the piles. The surface friction created by the settling of the backfilled earthen materials in contact with the surface facing of the piles tends to transmit a substantial amount of adverse vertical load to the pile. This load tends to adversely affect the piles, sometimes causing enough stress that the piles may bend or otherwise become deformed, affecting the integrity of the structure supported.
One technique for avoiding the application of the downward force from the backfill material against piles is to surround the piles with metal or plastic conduits prior to the backfilled earthen material being placed about the piles and to fill the tubes with sand, or the like. As a result, the downward settling movement of the backfilled earthen material is applied to the exterior surfaces of the conduit in lieu of the exterior surfaces of the pile. This technique generally protects the pile from the downward forces of the backfill earth.
While the aforementioned conduit and sand technique has been successful in avoiding adverse effects on bridge abutment piles, etc., due to the downward weight applied by the settling backfilled earthen materials, the use of the conduits and sand utilizing this technique is expensive in that the materials are relatively expensive, and the labor required to telescopically mount the conduits over the piles and then to fill the conduits with sand is expensive.
One technique for overcoming the aforementioned limitations is disclosed in U.S. Pat. No. 4,721,418, in which a pile jacket, formed of laminated sheet material, such as polyethylene, is placed about a pile. When the load or weight of the backfilled earthen material tends to settle, it tends to move the pile jacket downwardly with respect to the pile, with the interfacing surfaces of the pile and the pile jacket forming a slip plane. In this manner, the jacket shields the pile from the downward force exerted by the downwardly-moving backfill material during settlement. The patent discloses that a worker could coat either the outer surfaces of the pile, or the inner surfaces of the pile jacket, with a lubricant, such as grease, to reduce the friction within the slip plane. However, in practice, it has been found that grease or other lubricants attract debris during pile settlement, thereby actually increasing the friction within the slip plane. A drawback of the '418 pile jacket relates to the manufacture of the sheet material for the pile jacket. Polyolefin films exhibit a high degree of tackiness in their natural state. This tackiness creates a problem during the manufacturing process.
It is well known that certain polymers and additives can serve to reduce both static and dynamic coefficients of friction greatly. A sheet or spray coating of PTFE (poly tetra fluoro ethylene) possesses one of the lowest coefficients of friction known. Recently, it has been shown proven that diamonds covered with a graphene sheet has the lowest measured coefficient of friction. However; these techniques are more expensive and impractical to use. History has proven the need to work within practical and economic boundaries in most applications.
The need persists in the art for an improved pile jacket.